Intestines Flashcards
What are the 3 anatomical features that increased the surface area of the small intestines?
- Circular folds
- Villi (mucosa & submucosa)
- Microvilli (intestinal cells)
What comprises the brush border of the intestines?
Enterocytes + Microvilli
What happens if there is ischemia to the villi of the intestines?
Loss of brush border = lower absorptive capacity
What are the five cell types in the surface epithelium?
- Absorptive enterocytes
- Goblet cells
- Secretory enterocytes
- Endocrine cells
- Stem cells
Why are there stem cells in the small intestinal cells?
Rapid turnover
What is the function of Brunner’s glands?
Secrete mucus and HCO3
What is the function of the secretory enterocytes?
Help facilitate absorption by secreting H2O and electrolytes
“undisturbed water layer”
What are the cells in the crypts of Lieberkuhn?
Goblet
Secretory Enterocytes
Absorptive enterocytes
What is the function of the absorptive enterocytes?
Expresses a variety of enzymes that facilitate digestion
What are the primary regulators of small intestine motility, and do they stimulate of inhibit contractions?
- Ach (stim)
- VIP (inhibit)
- NO (inhibit)
What are the three types of intestinal motility?
- Migrating motor complex
- Segmental contractions
- Peristaltic contractions
What does distension in the small intestine trigger? What is the function of this?
Local and distal peristaltic relayed by a series of reflexes
Function = get things downstream moving
What is the stimulus for gastroenteric and gastroileal reflexes?
Distention
What regulates emptying of the intestines into the cecum?
Distension of the cecum inhibits relaxation of the sphincter, but distention in the ileum stimulates
What mediates the ileocecal sphincter reflex?
Inhibition is mediated through the ENS
What causes the haustra of the large intestine?
Organization of the smooth muscle (circular muscles and tenia coli)
Why is the smooth muscles organized as it is in the large intestines?
Facilitates mixing of fluids (and thus absorption)
Are there villi in the large intestines?
Nope
What are the primary sites of nutrient absorption in the large intestines?
Crypts
What are the three positive regulators of the Crypts of Lieberkuhn?
Mechanical
PNS
ENS
What is the negative regulator of the crypts of Lieberkun?
symp innervation
What happens to the Haustra during intestinal smooth muscle contraction? What is the function of this?
Become more prominent
Increases mixing
What is the function of symp stimulation in the distal colon?
Relaxas portions of the colon distal to the distension
What are the propulsive movements of the large intestines?
Mass peristalsis moves contents toward rectum 3 times /day
Where is the coloncolonic reflex initiated?
Where there is distension
Distention in what two places along the GI tract will induce mass movement?
Stomach and duodenum
gastrocolic and duodenocolic reflexes
What are the four key features to the defecation reflex?
- Intrinsic reflex
- Parasympathetic reflex
- Additional afferent signals
- Desired defecation
What is the intrinsic reflex of defecation? What division of the ANS is this initiated by?
Distention in the distal portions of the colon produces peristaltic wave toward the rectum. This is initiated by the ENS.
What causes the internal anal sphincter to relax?
ENS activity from distension leads to release of NO and VIP
What happens to the signal to contract in the external sphincter before defectation?
Increases
How strong is the ENS signals in the rectum for the defecation reflex?
Weak–parasymps more important
What is the effect of the PNS in the defecation reflex?
Signals from the rectum are relayed to the spinal cord, and back to the descending colon, forcing feces toward the anus
What is the role of the additional afferent signals from the rectum to the spinal cord in the defecation response?
Initiates a deep breath, closure of the glottis, and contraction of the abdominal wall to push fecal content downard
What happens to the pelvic floor during defecation?
Relaxes
What happens during the desired defecation stage of the reflex?
Conscious relaxation of the external sphincter, and evacuation of the feces
Which has folds: small or large intestines?
Both
Which has villi: small or large intestines?
Small
Which has microvilli: small or large intestines?
Both
Which has crypts/glands: small or large intestines?
Both
Which has nutrient absorption: small or large intestines?
Small
Which has water/electrolyte absorption: small or large intestines?
Both
What happens to the number of bacteria as you move from the stomach through the intestines?
Increases
What are the four factors that change the growth of gastrointestinal bacteria?
- GI secretions
- Mucosal immunity
- Intestinal motility
- Pharm agents
What are the five functions of intestinal bacteria?
- Conversion or primary bile to secondary bile
- Deconjugation of compounds conjugated in the liver
- Nutrient salvage
- Detox
- Suppression of pathogens
What happens to the effectiveness of oral contraceptives with abx use?
Decreases b/c rely on bacteria to break down estrogen
What increases the secretions of the Brunner’s glands and the crypt of Lieberkuhn?
Chyme
ENS
CCK
Secretin
What decrease the secretions of Brunner’s and crypts of Lieberkuhn?
sympathetics
Which muscles of the large intestines are tonically contracted: the longitudinal or the circular?
Circular
What is the function of the absorptive enterocytes in the large intestines?
Absorb H2O and electrolytes
What causes relaxation in the large intestines, as opposed to NO in the rest of the GI tract?
Symp stimulation
Goblet and absorptive enterocytes are located primarily (where?); while secretory enterocytes, endocrine cells, and stem cells are (where)?
Goblet and absorptive enterocytes = villi
Secretory enterocytes, endocrine cells, and stem cells= crypts
Segmental contractions of the intestines are important for what and are induced by what?
Important for mixing, and induced by distention
What type of contractions are utilized to push intestinal contents toward the anus?
Peristaltic
What causes the mixing movements in the large intestines?
Circular muscle contraction, resulting in bulging of the intestinal wall
What initiates the propulsive movements of the large intestines? How often do these occur?
These mass movements are initiated by a constriction point, causing a large portion of the intestines to contract.
What is the intrinsic portion of the defecation reflex?
Distension in the distal colon signals nerves to start peristaltic contraction, forcing fecal matter toward the anus
What is the parasympathetic defecation reflex?
After the intrinsic reflex, parasymp nerves to spinal cord cause mass peristalsis, and forcing feces against the anus
What is irritable bowel syndrome?
an idiopathic chronic relapsing disorder characterized by abdominal discomfort (pain, bloating, distension, or cramps) in association with alterations in bowel habits (diarrhea, constipation, or both).”
What is the treatment for IBS?
Exercise and symptomatic relief
What are the two types of inflammatory bowel disease?
Ulcerative colitis
Crohn’s disease
Which part of the GI tract is Crohn’s disease usually associated with?
ileum
Skip lesions = ?
Crohn’s disease
What is the site of origin of the inflammation in crohn’s disease?
Submucosa
Where does the inflammation of ulcerative colitis originate from?
Crypts of lieberkuhn
What are the complications of IBD? (2)
Arthritis
Vit deficiencies
What is Hirschsprung’s disease?
Congential Agangiolinc colon
